Preparation of glutaconic acid



Patented Oct. 15, 1940 2,218,il32 V PREPARATION or GLUTACONIC' Aon)Norman D. Scott, Sanborn, N. Y.,.assignor to E. I.

du Pont de Nemours.& Company, Wilmington, DeL, a corporation of DelawareNo Drawing. Application October 2,1939,

Serial N0..297,431 j 7 Claims. (Cl. 260- 537) This invention relates toa method for preparing glutaconic acid.

This application is a continuation-in-part of my copending applicationSerial No. 228,003, filed September 1, 1938.

Heretofore glutaconic acid has been obtained from alpha-hydroxy-glutaricacid or ester by dehydration. or by saponification ofbeta-hydroxy-glutaronitrile or alpha-acetyl glutonic ester. It has beenfurther suggested to' prepare glutaco'nic' acid by decarboxylation ofdicarboxy glutaconi'cester or isoaconitic ester, by thermaldecomposition of pyrazoline dicarbonic ester, and also by fission of anumber of cyclic'acids or esters'such as coumalic acid or ethoxypyronedicarbonic ester. These known processes,-however, are more or lessrestricted to laboratory use only, since the starting materialsthemselves are not available in appreciable quantities.

An object of the present invention is an improved method for preparingglutaconic acid; .A further object is to prepare glutaconic acid fromrelatively inexpensive raw materials. Otherobjects will be apparent fromthe present disclosure.

I have found that glutaconic acid can'be prepared in good yields whensubjecting propiolic acid or its salts to the action of aqueoussolutions of certain alkaline reagents.- Propiolic acid may readily beprepared by carboxylation of sodium acetylide, thus utilizing therelatively inexpensive raw materials, acetylene, sodium and carbondioxide. Although the reaction mechanism is not definitely known, it isbelieved that propiolic acid salts are hydrolyzed and condensed in thealkaline medium and then split off formate, yielding the glutaconic acidsalt. Thus sodium propiolate CHECCOONa in alkaline solution istransformed into the sodium salt of glutaconic acidNaCOzCI-I2CI-I=CHCO2Na which can be easily transformed into glutaconicacid by acidification, e. g. with dilute sulfuric acid.

The alkaline materials to be reacted with the propiolate in accordancewith my invention are the alkali metal hydroxides, the alkaline earthmetal hydroxides and water-soluble quaternary organic ammoniumhydroxides. Examples of the latter suitable for my invention aretetraalkyl ammonium hydroxides, such as tetramethyl ammonium hydroxide,tetraethyl ammonium hydroxide and dimethyl, diethyl ammonium hydroxide.

A convenient way for carrying out my invention consists in heating asodium propiolate solution with about two molecular proportions ofsodium hydroxide at about 60 C. for about 6 hours and acidifying theresultant mixture with dilute sulfuric acid. The resultant glutaconicacid then can be extracted with ether or the like.

Although any propiolic acid salt can be used for the process of myinvention, I prefer to use.

salts which are prepared from purified propiolic acid; more particularlythe alkali metal salts prepared from such purified propiolic acid, sincethe salts prepared from purifiedpropiolic acid give a purer glutaconicacid which can be more readily separated from the reaction mixture thanwhen prepared from crudepropiolate. Of course, it is not necessary tointroduce the propiolate as such into the alkaline solution but thepropiolate can be also formed by the-reaction of the alkaline reactionmedium and thepro-piolic acid. Thus whenpropiolic acid is added. to asodium hydroxide solution, sodium propiolate is formed which then isacted on by the remaining caustic solution. The propiolate and alkaliboth should be in solution. I, v

My inventionis' further illustrated by'the following examples:

Y Example I v 50.8..grams of propiolic acid (94.8%, i. e. 1 mol) weredissolved in;340 cc..water. 322 cc. of 9.3 N sodium. hydroxide;(3' mol)were added to the propiolic acid solution, while cooling to l020 C. Thereaction mixture was then placed under nitrogen atmosphere, by. passingnitrogen through the-reaction vessel and the reaction mixture was heatedto .60 C. for 6 hours. The reaction mixture then was cooled to 10 to "vC. and acidifiedbygadding dropwise 360 cc. of diluted sulfuric acid,containing 60 cc. of concentrated sulfuric acid. The acidified mixturewas saturated with ammonium sulfate and repeatedly extracted with washedether. The extract was dried with magnesium sulfate, filtered andevaporated in vacuo at 85 to 95 C. Thus a yield of 23.7 grams of crudeglutaconic acid, i. e. a 73% yield based on the propiolic acid used wasobtained.

Example II The process described in Example I was repeated, but usingother alkaline reagents in place of the sodium hydroxide. The followingresults were obtained:

If desired, the crude glutaconic acid can be recrystallized inclichlorethyl ether or other solvent, by which method about 82% of thecrude gluta- ,conic acid can be recovered as pure glutaconic acid.

My invention is not restricted to the specific procedure of the examplesand is to be understood in its broad scope as defined in the appendedclaims. However, it has been found that the formation of glutaconic acidoccurs most readily within a temperature range of about 40 to 100 C. andI prefer to carry out the process of my invention at about 60 C. Theratio of alkaline substance to the propiolate may vary widely; ingeneral the rate of reaction will increase as the ratio of alkali topropiolate and the concentration of the alkali are increased.Preferably, the molar ratio of alkali to propiolate should be about 1 to3 mols of the alkali to one mol of the propiolate. For example, it hasbeen found that when using sodium hydroxide as the alkaline reactionmedium a molecular ratio of about 1.5 to moles of sodium hydroxide toone mole of the propiolic acid salt is especially suitable, or in thecase of propiolic acid, aratio of about 2.5:1 to 3.511, one mole of thehydroxide being consumed for neutralization of the acid. When usingother alkaline reaction mediums, for example, other alkali metalhydroxides such as potassium hydroxide, alkaline earth hydroxides or thesoluble quaternary organic ammonium hydroxides, equivalent amountsgiving about the same alkalinity may be used. Solutions being about 2.5to 2.7 normal with respect to sodium hydroxide have been foundespecially advantageous; lower and higher concentrations, however, maybe utilized if desired without departing from the spirit of myinvention. High alkali concentrations, however, may lead to too violentreactions and the formation of undesired by-products. The termglutaconic acid as used in the claims includes also the salts ofglutaconic acid which can be easily transformed into the acid proper byacidification.

I claim:

1. The method of preparing glutaconic acid which comprises subjectingpropiolic acid in solution to the action of an alkaline reagent selectedfrom the group consisting of alkali metal hydroxides, alkaline earthmetal hydroxides, and watersoluble quaternary organic ammoniumhydroxides.

2. The method of preparing glutaconic acid which comprises subjecting analkali metal salt of propiolic acid in solution to the action of analkaline reagent selected from the group consisting of alkali metalhydroxides, alkaline earth metal hydroxides, and water-solublequaternary organic ammonium hydroxides.

3. The method of preparing glutaconic acid which comprises subjectingpropiolic acid in solution to the action of an alkaline reagent selectedfrom the group consisting of alkali metal hydroxides, alkaline earthmetal hydroxides, and watersoluble quaternary organic ammoniumhydroxides at a temperature within the range of about 40 to 100 C.

4. The method of preparing glutaconic acid which comprises subjectingpropiolic acid in solution to the action of an alkali metal hydroxide ata temperature within the range of about 40 to 100 C., the molecularratio of the alkali metal hydroxide to propiolic acid beingsubstantially in excess of 1:1.

5. The method of preparing glutaconic acid which comprises subjectingpropiolic acid in solution to the action of an alkali metal hydroxide ata temperature within the range of about 40 to 100 C., the molecularratio of the alkali metal hydroxide to propiolic acid being about 2.5:1to :1.

7 6. The method of preparing glutaconic acid which comprises subjectingpropiolic acid in solution to the action of an alkali metal hydroxide ata temperature of about 60 C., the molecular ratio of the alkali metalhydroxide to propiolic acid being about 2.5:1 to 3.5: 1.

7. The method of preparing glutaconic acid which comprises subjectingpropiolic acid in solution to the action of sodium hydroxide at atemperature of about to 100 0., the molecular ratio of sodium hydroxideto propiolic acid being about 2.5:1. to 3.521, and the solution beingabout 2.5 to 2.7 normal with respect to the sodium hydroxide. NORMAN D.SCOTI.

